"Jerry Martes" wrote in message .. .
I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google search.
Does anyone know of any publication that show how someone has already worked
out the problems of contructing one?

Seems like the postings I've seen here are off on the wrong foot.
Yep, there will be problems, but I've learned a lot more by building
and experimenting with things that didn't work, than listening to or
arguing with people telling me that they won't work. And in fact, a
lot of the time they DO work well enough for me to accomplish what I
wanted.

So I'd like to encourage Jerry to have a go at the copper-pipe slotted
line, keeping in mind the pitfalls that have been mentioned and
thinking of ways around them. I know I would have no trouble at all
making a uniform narrow slot in such a pipe, maintaining a radial
angle straightness well under a degree, without using a milling
machine. I know I'd have no trouble supporting the 7/8" diameter
center conductor to maintain the impedance within a fraction of a
percent over the line length. With proper geometry, sag would not be
an issue for coupling. (Keeping the line vertical is one way, but not
the only way.) Perhaps more important is the initial straightness of
the pipes. 3/4"nom pipe is stiff enough that I can see doing this
with support only at the ends, so impedance AND velocity factor
variation caused by dielectric supports are no longer issues.

Will everything go smoothly? Heck no! Will Jerry learn from doing
it? You bet! Go for it, Jerry, and please see if you can write up
something about your results, to share with others. Listen to the
advice you get, but make up your own mind about what will work best
for you. You should be able to make very decent estimates of the
effects from the problem areas folk have mentioned, through either
formulas or measurements or both. You should be able to make tests on
your line to see if it's performing like you think it is, by applying
known loads and testing at various frequencies, using assorted
detectors and probes.

Cheers,
Tom